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POM > Hypersensitivity > Flashcards

Hypersensitivity Flashcards

1
Q

What is an antigen?

A

Any molecule that can be recognised by an antibody or the adaptive immune system.

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2
Q

What does IgE do in relation to mast cells?

A

Primes mast cell.

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3
Q

What is the only class of antibody that can cross the placenta?

A

IgG

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4
Q

What class of antibody can cross muscosal epithelium?

A

IgA and sometimes IgM.

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5
Q

What immunoglobulin activates classical complement pathway?

A

IgM and IgG3.

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6
Q

What class of antibody binds to Fc receptors on phagocytes?

A

IgG

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7
Q

What class of antibody is present on membrane of mature B cells?

A

IgM.

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8
Q

What is type I hypersensitivity mediated by?

A

IgE.

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9
Q

Which T helper cells activate B cell in type 1 hypersensitivity?

A

Th2 and T follicular helper cells.

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10
Q

What cytokines cause B cells to produce IgE (class switch) in type 1 hypersensitivity?

A

IL-4 and IL-13.

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11
Q

Which innate immune system cells have a high affinity for IgE?

A

Mast cells and basophils.

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12
Q

What cells are seen in early phase of type 1 hypersensitivity?

A

Mast cells.

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13
Q

What is seen later (within few hours) on in type 1 hypersensitivitiy?

A

Recruitment of neutrophils.

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14
Q

What do we seen in late response (3-5 days) to type 1 hypersensitivity?

A

High frequencies of eosinophils.

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15
Q

What does type II hypersensitivity involve?

A

Destruction of cells by IgG or IgM antibody bound to antigens present on the surface of the cells.

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16
Q

How can antibodies cause type 2 hypersensitivity?

A

Activation of complement system (C3a, C4a and C5a) recruit neutrophils which can destroy cells by degranulation. Formation of MAC complex (C5b, C6-C9) which can creates a channel in cell membrane leading to lysis. Opsonisation and phagocytosis. Antibody dependent cell mediated cytotoxicity where NK cells bind to fc region and release toxic granules. Antibody mediated cellular dysfunction where antibody binds to receptor blocking it or activating it.

17
Q

What is type 3 hypersensitivity?

A

Immune complex driven disease. Immune complexes cannot be efficiently cleared, immune complexes end up being deposited in the blood vessel walls and tissues, promoting inflammation and tissue damage.

18
Q

How can type 3 hypersensitivity lead to tissue damage?

A

Activation of complement system (C3a,C4a,C5a) increase vascular permeability which can lead to oedema. Neutrophils can’t phagocytose complexes and so degranulate which can lead to vasculitis.

19
Q

What is an immune complex?

A

Non-cell bound antigen-antibody complexes which are normally cleared through the activity of the immune system.

20
Q

What class of disease involve type 3 hypersensitivity?

A

Auto immune disease.

21
Q

What is type IV hypersensitivity?

A

Delayed type hypersensitivity involving T cells.

22
Q

How quick is type I hypersensitivity?

A

Immediate.

23
Q

What is the first exposure to an allergen called in type 1 hypersensitivity?

A

Sensitization.

24
Q

What causes mast cell to degranulate in hypersensitivity 1?

A

Cross linkage of IgE primed mast cell.

25
Q

Why does anaphylaxis happen in type 1 hypersensitivity?

A

Release of histamines from mast cells cause blood pressure drop.

26
Q

Difference between type II hypersensitivity and type III?

A

Type II involves antibodies binding to antigens on cell surfaces while type III involves antibodies binding to soluble molecules to form complexes. Type 2 inflammation occurs where antigen is present in the body while type 3 is where the antigen-antibody complexes are deposited. Type 2 small amount of complement is produced while type 3 lots of complement proteins are released. Levels of complement protein can be tracked to see progression of type 3 hypersensitivity.

27
Q

Why is type IV delayed?

A

Memory T cell response is slightly slow. 48 -72 hours.

28
Q

What causes contraction of pulmonary smooth muscle?

A

Leukotrienes and prostaglandins.

29
Q

What are the rate limiting molecules in all hypersensitivity reaction?

A

Antigens.

30
Q

What are the characteristics of the infiltrate in a delayed hypersensitivity reaction?

A

An infiltrate composed of helper T cells and macrophages.

31
Q

What is a hapten? Give an example

A

A small molecule which on its own is not antigenic, but when associated with a large carrier such as a protein can form an antigen. Penicillin binding to surface antigen on red blood cells causing haemolysis.

32
Q

When is a coombs test done?

A

Autoimmune hemolytic anemia. Drug-induced immune hemolytic anemia.

33
Q

Describe and explain the coombs test

A

Blood sample from patient is taken. Red cells from patient are washed to remove any unbound antibodies. Coombs reagent (anti human globulin) is added. If antibody is present on the surface of the red blood cells this results in agglutination.

POM (41 decks)

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